The invention relates to a process and an apparatus for performing both chemical reactions and separation by distillation of the reaction mixture obtained. These procedures are known as reactive distillation or catalytic distillation, when the chemical reaction takes place in the presence of a catalyst.
They are more particularly applied to the preparation of tertiary alkyl ethers such as methyl tert. butyl ether (MTBE), methyl tert. amyl ether (TAME), ethyl tert. butyl ether (ETBE) or ethyl tert. amyl ether (TAEE), by catalytic reaction of the appropriate olefin (isobutene or isopentene) with the appropriate alcohol (methanol or ethanol), as a function of the particular case.
They can also be applied to the alkylation of benzene by catalytic reaction with the appropriate olefin, e.g., ethylene or propylene, in order to form the corresponding alkyl benzene, e.g., ethyl benzene or isopropyl benzene.
With more particular regard to the etherification reactions by reactive distillation, various processes have already been proposed in the prior art and in particular in U.S. Pat. No. 3,629,478, EP-A-008860, FR-A-2,503,700 and FR-B-2,628,737.
U.S. Pat. No. 3,629,478 teaches the use of distillation trays and of only loosely placing the catalyst only in the liquid down pipes of said distillation trays, so as to avoid the disturbing effect of the vapour phase through the catalyst. However, the presence of the catalyst in such down pipes leads to a pressure drop, so that the liquid prefers to descend in countercurrent in the orifices provided for the vapor on the work table of each distillation tray, rather than pass through the catalyst, which is consequently placed out of circuit.
The European Patent 0008860 proposes the use of a distillation column filled with an appropriate catalyst for the preparation of methyl tert. butyl ether (MTBE), in which the catalyst also acts as a packing for the distillation, thus forming the MTBE and separating it at the same time from the constituents having four carbon atoms. Although the process described leads to a significant technical contribution in the reactive distillation field, the contact between the liquid phase and the catalyst is intermittent to a varying extent as a result of the disturbing effect of the vapor phase.
The French Patent 2,503,700 proposes the use of a series of catalytic stages with an upward vapor-liquid circulation in the catalyst bed, the catalyst being immersed. However, the distillation effect is not as good as expected. Moreover, a hydrodynamic problem can arise because, due to gravity, it will no longer be easy for the liquid to rise through each catalyst bed.
The French Patent 2,628,737 proposes a technology for bringing about an alternation of the distillation and reaction zones in such a way that in a reaction zone only the liquid phase traverses the catalyst bed in the downward direction. This technology suffers from the disadvantage of requiring, for optimum operation, each distillation zone to have, in addition to one or more conventional distillation trays, a distribution tray and a redistribution tray for the liquid, which increases the height of the column and therefore its costs.
Canadian Patent Application 2,043,819 describes a reactive distillation column having a zone in which are concurrently performed a catalytic reaction and the separation by distillation of the products of said reaction, said zone having reaction "trays" supporting a particulate catalyst and distillation trays, more particularly of the bubble tray type, coupled with the reaction trays by means of a continuous liquid mass immersing, in its lower zone, the said catalyst and, in its upper zone, the said distillation tray. The reaction tray has a stack for supplying the vapor rising from the zone located below the "coupled" assembly to a vapor distributor located below the distillation tray. The height of the liquid mass between the reaction tray and the distillation tray must be adequate to prevent the entrainment of catalyst particles. The liquid phase flows from the upper part of the coupled assembly by flowing over an overflow via a down pipe either to a conventional distillation tray, or to another "coupled" assembly located below the "coupled" assembly in question. In the same way, the reaction tray of a coupled assembly is supplied with liquid phase by a down pipe resulting from flowing over an overflow either from a conventional distillation tray, or from another "coupled" assembly located below the "coupled" assembly in question.
In summarizing, the "coupled" assembly described in this document consists of a bubble tray, in whose bottom is deposited the catalyst, the bubble stack having been extended to take account of the presence of the catalyst mass and its height.